煤粉云火焰传播特性实验研究

煤矿开采中存在煤粉爆炸的重大安全隐患,本实验主要研究煤粉云的火焰传播,为预防和控制煤粉爆炸事故提供理论依据.实验采用粉尘云点火装置对煤粉在燃烧玻璃管中进行试验,通过改变煤粉云浓度探讨其对煤粉云火焰传播过程的影响,并利用高速摄影记录煤粉火焰传播过程.结果表明,点火电极在点燃煤粉云后,火焰沿着玻璃直管管壁竖直传播,火焰在传播过程中发出明亮的黄光并在玻璃直管上端端口形成蘑菇云状的火焰.当煤粉云的浓度为250 g/m3时,其燃烧时间远远小于浓度为500 g/m3和750 g/m3时的燃烧时间.当浓度分别为250 g/m3、500 g/m3和750 g/m3时,其火焰前锋阵面最大传播速度分别在100 ms、353 ms和310 ms时达到相应的最大值1.51 m/s、2.00 m/s和1.61 m/s.火焰前锋阵面达到最大速度的时间和火焰传播的最大速度随浓度的增加先增大后减小.     

Numerical Calculation of Minimum Ignition Energy for Hydrogen and Methane Fuels

Minimum ignition energies of hydrogen/air and methane/air mixtures have been investigated numerically by solving unsteady one-dimensional conservation equations with detailed chemical kinetic mechanisms. Initial kernel size needed for numerical calculation is a sensitive function of initial pressure of a mixture and should be estimated properly to obtain quantitative agreement with experimental results. A simple macroscopic model to determine minimum ignition energy has been proposed, where the initial kernel size is correlated with the quenching distance of a mixture and evaluated from the quenching distance determined from experiment. The simulation predicts minimum ignition energies of two sample mixtures successfully which are in a good agreement with the experimental data for the ranges of pressure and equivalence ratio.     

Observation of coal fragmentation in early stages of combustion

Measurements of coal fragmentation in the early stages of combustion were undertaken in the size range of crushed coals for Chinese Dongjin and Indonesian Roto coals. A flat flame burner fed with a premixed mixture of methane, air and partly hydrogen was used for the burning of a single coal particles. A high speed video camera system was used for the observation of coal fragmentation during approximately 80 msec. Fragmentation is consistently observed in the controlled combustion environment over a gas flame temperature range of 1220K–1320K. The data indicate that a single coal particle often disintegrates into two, three, and sometimes more fragments. The dominant mechanisim of fragmentation is that producing two fragments in primary fragmentation. The Dongjin coal breaks up more extensively than the Roto coal with the frequency of fragmentation exhibiting a strong particle size dependence and a weaker gas flame temperature dependence. The mean time of primary fragmentation for the Dongjin coal falls to between 10 msec and 20 msec and does not remarkably vary with particle size and gas flame temperature. The mean time of primary fragmentation for the Roto coal is strongly dependent on the particle size, whilst shows less gas flame temperature dependence.     

一种研究柴油甲醇双燃料的定容燃烧弹试验装置

设计并研制了一种定容燃烧弹试验装置,用于对柴油在甲醇/空气预混均质混合气中燃烧特性的基础研究。介绍了该试验装置的各子系统的原理、结构及特点。定容燃烧弹试验结果表明:甲醇抑制了柴油的着火燃烧,随着甲醇/空气混合气浓度的增大,燃烧火焰变暗,碳烟生成受到抑制。与空气热氛围相比,甲醇/空气混合气氛围延长了柴油的滞燃期,加长了火焰的浮起长度。火焰稳定后,甲醇氛围中火焰的浮起长度随时间的变化比在纯空气氛围中大。     

Explosion characteristics of combustible wood dust in confined system: Analysis using oxygen consumption energy

The explosion characteristics, such as maximum explosion pressure, rate of explosion pressure rise, explosion efficiency, were investigated to determine the roll and significance of oxygen consumption energy in dust explosion. Dust explosion experiments were conducted in a Siwek 20L spherical explosion apparatus for three wood dust samples from a wood-based panel production factory. Unlike gas explosions having maximum explosion pressure at near chemical stoichiometric concentration, both the maximum explosion pressure and the maximum rate of explosion pressure of wood dusts appeared at three times or much higher equivalence ratio. Although there were differences in particle size among tested dusts, in the case of dust of which the mean particle size was not larger than 100 µm, P_max appeared at lower equivalent ratios when mean particle sizes were smaller and at higher equivalent ratios when mean particle sizes were relatively larger. Explosion efficiency for all dusts are around 10 %, of which the value is relatively lower than most of other normal combustion, which signifies dust explosion remains 90 % of unburned dust with high fire risks after explosion. In a dust explosion, it is difficult to estimate the weight of suspended dust participating in explosions, especially in fuel rich conditions, so a method for estimating explosion overpressure by applying oxygen consumption energy based on unit volume (1 m³, SAPT condition) was newly proposed and verified from the result of explosion efficiency. To practically apply these results to dust treating industry, the assessment procedure for dust explosion influence has been provided by introducing TNT equivalent model and its scaled distance.

     

An experiment of the combustion characteristics with laser-induced spark ignition

The combustion characteristics and minimum ignition energies using laser-induced spark ignition were demonstrated for quiescent methane-air mixtures in an optically-accessible, constant volume combustion chamber. Initial pressure and equivalence ratio as well as spark energy were varied in order to explore the flame behavior with laser-induced spark ignition. Shadowgraphs for the early stages of combustion process showed that the flame kernel becomes separated into two, one of which grows back towards the laser source. Eventually after a short period, the two flame kernels developed into two flame fronts propagating individually, which is unique in laser-induced spark ignition. For a given mixture, lower initial mixture pressure and higher spark energy resulted in shorter flame initiation period and faster flame propagation. The results of minimum ignition energies for laser ignition shows higher values than electric discharge results, however, the difference decreases toward lean and rich flammability limits.     

液压支架用大流量安全阀性能分析

安全阀是液压支架的重要保护元件，基于综采工作面上覆岩层的“砌体梁”结构力学模型，液压支架承受的是静态负载和动态负载的总和，基于此，提出了安全阀动静组合加载试验台（其中蓄能器的载荷模拟静态载荷，气体爆炸产生的载荷模拟动态载荷）。实验初始条件如下：LPG-空气混合气体爆炸前的压力为1.6 MPa,安全阀的调定压力为45 MPa,蓄能器的充液设定压力为31.5 MPa。实验结果表明：被试安全阀压力超调量为5 MPa，约为调定压力的11％，被试安全阀压力稳定时间为0.017 s。采用ANSYS Fluent对安全阀的流场进行仿真，通过高速摄像机得到了安全阀溢流过程的照片，验证了安全阀流场的仿真结果。     

高浓度粉体气力输送特性试验研究

在高浓度粉体气力输送试验台上,以压缩空气为输送介质,进行了两种粉体(黄沙、煤粉)的高浓度输送试验。试验结果表明,物料输送量和流化罐压力随着流化空气量的增加而增加;流化罐出口物料固气质量比随着流化空气量的增加而减小。试验还得到了物料输送量与流化空气量的关系式。     

水平管道中瓦斯爆炸火焰传播速度测量

在煤炭工业中, 瓦斯爆炸事故经常发生, 造成了巨大的人员伤亡以及材料性能的破坏. 在研究瓦斯爆炸机理过程中, 火焰前端传播速度是最重要的因素之一. 根据中北大学水平管道实验装置设计了一套火焰速度测量系统, 用于研究在密闭管道内圆环障碍物的数量和阻塞比对火焰传播速度的影响. 结果表明, 障碍物对瓦斯爆炸产生的火焰具有明显的加速作用. 随障碍物数量和阻塞比的增加, 火焰加速更加明显且持续更剧烈. 其中, 障碍物数量对火焰加速持续的作用更大, 而障碍物阻塞比的作用不明显.     

智能化喷雾降尘技术研究

传统的喷雾装置不能有效地降低空气中的粉尘.针对现有生产矿井由于采煤机械化程度提高带来的煤尘增加和具有煤尘爆炸性的特点,设计研究了智能化喷雾,采用感应旋转式装置,当粉尘浓度超过设定值时,粉尘浓度传感器报警.这样既做到了全面除尘又节约了水资源,为工作面创造了良好的、安全的生产环境,有很好的推广价值.     

变进气压力条件下发动机压缩空气制动过程分析

针对单级储能的气动-内燃混合动力发动机能量回收效果随储气罐压力增高而降低的问题,将双储气罐储能的技术方案应用到气动-内燃混合动力发动机中,初步得出了双储气罐储能系统可以通过改变进气压力来提高能量转化率COP(coefficient of performance)的观点。基于变质量热力学理论建立了压缩空气循环数学模型,并通过台架试验进行了初步验证。通过对模型进行稳态仿真,分析了进气压力、储气罐压力对压缩制动过程的影响。研究结果表明,进气压力与储气罐压力的变化对每循环回收气体质量的影响呈线性;储气罐压力与进气压力的比值是影响制动能量转化率的关键因素,能量转化率(COP)随储气罐压力与进气压力比值的升高而降低。     

Investigations of the watershield effect on blast waves: One and two-dimensional study

The object of this analysis is to investigate the mitigation effects of watershield on blast waves numerically. One application of current work is to resolve the design concerns for the ammunition storage facilities. To verify the numerical procedure using a multimaterial Eulerian finite element method, the results are compared with the available experimental data for detonation in a pressured tank, and the analytical predictions for air shocks. Features of the free-field detonation process are then studied from a series of one-dimensional simulations. The magnitude of peak pressure decreases and shock arrival time increases with increasing thickness of watershield. For design analysis, the case of two-dimensional axisymmetric geometry (a vertical) right-circular cylinder) with a central charge is also considered. The full process including initial detonation, shock wave propagation and reflection from the outer rigid boundary is examined. For the explosives immersed in water, the magnitude of peak pressure becomes smaller than those in air tank without watershield. At later time period, the average gas pressure left in the air tank is about 20 bar.     

液氢温区冷氦增压试验系统的设计

针对液体火箭冷氦增压系统试验研究的不足,设计并建设了液氢温区冷氦增压试验系统,采用深低温制冷机组配合高压低温换热贮罐来实现液氢温区高压冷氦气源;使用管壳式加热器真实模拟箭上换热器的换热性能与流阻;提出以排气方式模拟贮箱推进剂消耗过程中压力的变化情况。该试验系统安全可靠,更加真实地模拟了液体火箭冷氦增压系统的工作过程。     

Instrument safety in explosive atmospheres.

The current "Energy Crisis" has dramatically increased our potential need for coal, the worlds most abundant fossil fuel. This will probably lead to a greater use of automation and instrumentation in the coal mining industry. The presence of methane in coal mines and in the coal itself plus the presence of coal dust, both of which can form an explosive atmosphere in air, means that the possibility of a gas or coal dust ignition must be considered when designing, purchasing and installing new equipment in this industry. In addition, many metallurgical processes involve the use of potentially explosive substances against which similar safety precautions must be taken. This paper outlines the various methods of protection currently in use and proposed for electrical instruments in explosive atmospheres, with particular emphasis on the work of the International Electrotechnical Commission.     

基于相干反斯托克斯拉曼散射的二维温度场扫描测量

开展了基于相干反斯托克斯拉曼散射(CARS)技术的二维温度场扫描测量研究。通过同步扫描测量点及信号接收端的方式,实验测量了甲烷/空气预混火焰水平截面离散点的温度,并插值重建了二维温度场;用同步扫描法调节测量点与火焰的位置,实现了在扫描过程中对火焰同一空间位置的温度测量,排除了火焰空间分布不均匀性对扫描测温结果的附加影响。最后分析了提出的扫描CARS测量系统在实验设定状态下的扫描测温A类不确定度。结果显示:在扫描测量同一空间位置的实验中,测得该点平均温度为2 074K;测温A类不确定度优于21K。本研究量化了扫描CARS温度测量系统的不确定度,提高了扫描温度测量结果的可信度,为后续稳态火焰温度分布高精度测量、计算机流体动力学(CFD)模拟验证及燃烧基本问题研究奠定了实验基础。     

Atomization of fuel mixtures

The combustion process of a coal/oil slurry begins by atomization of the slurry. This project is a presentation of experimental system and results on atomization of coal/oil(COM) and coal/methanol mixtures with a twin-fluid and a wheel atomizer. The slurries are consisted of coal/methanol and coal/oil mixtures with two different concentrations and two coal particile sizes. The volume median diameters of the coal particles were 45 and 130 microns. The oil was No. 2 diesel oil. The droplet size was determined by photographing the spray and the photographs were analyzed to determine droplet size and distribution. The results show that the inclusion of particles in the liquid(both methanol and diesel oil) does not appreciably affect the atomized droplet size. The tendency is for the slurry droplets to be somewhat smaller than the droplets atomized with the pure liquid.     

Effects of pressure and carbon dioxide,hydrogen and nitrogen concentration on laminar burning velocities and NO formation of methane-air mixtures

We studied the effects of increasing pressure and adding carbon dioxide, hydrogen and nitrogen to Methane-air mixture on premixed laminar burning velocity and NO formation in experimentally and numerically methods. Equivalence ratio was considered within 0.7 to 1.3 for initial pressure between 0.1 to 0.5 MPa and initial temperature was separately considered 298 K. Mole fractions of carbon dioxide, hydrogen and nitrogen were regarded in mixture from 0 to 0.2. Heat flux method was used for measurement of burning velocities of Methane-air mixtures diluted with CO₂ and N₂. Experimental results were compared to the calculations using a detailed chemical kinetic scheme (GRI-MECH 3.0). The results in atmosphere pressure for Methane-air mixture were calculated and compared with the results of literature. Results were in good agreement with published data in the literature. Then, by adding carbon dioxide and nitrogen to Methaneair mixture, we witnessed that laminar burning velocity was decreased, whereas by increasing hydrogen, the laminar burning velocity was increased. Finally, the results showed that by increasing the pressure, the premixed laminar burning velocity decreased for all mixtures, and NO formation indicates considerable increase, whereas the laminar flame thickness decreases.     

On-line measurement of oil/gas/water mixtures,using a capacitance sensor

This paper describes the use of a non-intrusive capacitance transducer for the simultaneous on-line measurement of water and undissolved gas in crude oil. The water concentration of the flow is determined from the mean capacitance of the flowing mixture. The same transducer can be used simultaneously to determine the void fraction of the flow by measuring the instantaneous variation in the permittivity of the mixture created by fluctuations of the gas component. There is an interaction between these two measurements but this can be decoupled. This measurement principle was investigated experimentally, using process oil/water/air mixtures. Results are reported for mixtures with water contents up to 40% v/v and void fractions up to 15% v/v.A three-component volumetric flowrate measurement system, based on the capacitance transducer discussed in this paper was proposed. The work reported and the conclusions drawn relate to tests using mixtures of lubricating oil/fresh clean water/air. No work has so far been carried out in mixtures of crude oil/saline waters/hydrocarbon gases typical of the intended applications, nor have estimates been made of the effects that the variable nature of these actual components might have on the performance of the technique. Also, the tests were made on a Perspex section of pipe at nominal pressure whereas the real-life application would require measurements on a high-pressure/high-integrity stell pipeline; the practical problems of adapting the technique to the latter situation have not been examined though they are considered to be resolvable.     

压缩空气净化设备的选用

就太钢炼铁厂喷煤工程中喷吹工艺用压缩空气的净化方式作出选择， 并对空压站关键设备的选型进行分析。在满足处理气体参数要求的前提下， 达到技术先进， 选型可靠， 价格可行， 适应新技术发展的目的。     

Laminar flame speeds for n-butanol/air mixtures at elevated pressures and temperatures: An experimental and numerical study

Laminar flame speeds of n-butanol/air premixed flames were measured experimentally and numerically at elevated pressures and temperatures for a wide range of equivalence ratios. Laminar flame speeds were obtained experimentally from the temporal evaluation of the flame front of spherically outwardly propagating flames at zero stress rate. The shadowgraph technique was employed to gain optical access to the constant volume combustion chamber. Flame propagation images were captured by a high-speed camera and MATLAB codes were used to process the images and calculate laminar flame speeds. Flame speeds have been calculated numerically using CHEMKIN-Pro based on a short reaction mechanism for n-butanol oxidation, which was derived from a previously published full reaction mechanism. Numerical predictions were in qualitative agreement with experimental data. The effects of initial pressure and temperature elevation were analyzed. Also, the effect of simultaneous elevation of initial pressures and temperatures is documented. For all experimental conditions, the maximum flame speed was found at around equivalence ratio 1.1. In general, flame speeds decreased with the elevation of initial pressure and increased with initial temperature elevation.